This invention relates to a process for treating a feedstock obtained from a retort process and, in particular, to a process for separating water and solids from shale oil feedstock obtained from a shale retort process.
Oil feedstocks produced by retort processes and in particular, shale retort processes, generally contain a large amount of water and insoluble solids. In most cases, it is difficult to remove the water and insoluble solids from the feedstock to a sufficient extent to permit recovery and use of the oil. It is particularly desirable to recover oil of sufficient purity to allow the recovered oil to be used as a fuel.
Specifically, in the case of shale oil obtained from a shale retort process, shale fines become entrained in the oil and are difficult to separate. The present invention is particularly suitable for separating shale fines from shale oil.
A shale retort process is disclosed in Brazilian Pat. No. PI 7105857. According to the process disclosed, hydrocarbon containing solids are continuously fed at the top of a vertical retort. The solids are evenly distributed to the retort zone and then proceed downwards to a cooling zone, located below the retort zone. Retorting is carried out at superatmospheric pressure as follows:
1. Recycled gases that had previously and indirectly been heated from an external source and which are substantially devoid of free oxygen are introduced through the bottom of the retort zone at the retorting temperature; and,
2. Recycled gases which are substantially devoid of free oxygen are introduced cold into the bottom of the cooling zone. The cold recycled gases travel upward and exchange heat with the solid retorted material. The solid retorted material is continuously removed through the bottom of the retort zone and the retort products are removed from the top of the zone. The retort products consist primarily of oil in the form of mist and gas. In the process, it is essential to provide direct contact between the gas and the solids in order to achieve proper retort operation. The gaseous effluents carry the oil extracted from the shale out of the retort. In addition, undesirable amounts of dust are extracted from the shale by the gaseous effluents.
Attempts to reduce the volume of fines entrained with the oil by pretreatment of the retort feed generally are inadequate. Shale fine generation occurs during the retort process itself. These fines are not fully retained in the cyclones and precipitators. Accordingly, the oil obtained from prior art processes has an unacceptable water and solids content for conventional use as a fuel.
Many papers have been published suggesting a wide variety of solutions to the problem of fines entrained with oil. Some authors suggest the use of chemical additives capable of picking up the solid particles in a non-oil phase. Phase separation methods are also suggested. U.S. Pat. No. 3,929,625 teaches the use of a chemical additive that is capable of forming a dispersion with the oil. The dispersion is then subjected to an electric field to break it up.
Other processes are based on solvent extract methods combined with settling, filtration and/or distillation steps and the like. Examples of such methods are shown in U.S. Pat. Nos. 4,094,781 and 4,162,965. Another exemplary method is shown in Canadian Pat. No. 1,094,484 and other methods are also known. However, all of these prior art methods are less than completely satisfactory.
Accordingly, it is desirable to provide a satisfactory process for separating water and insoluble solids from a fuel oil feedstock.